This application is based on application No. 00-0376640 filed in Japan, the contents of which are hereby incorporated by reference.
The present invention relates to the field of art of image forming apparatuses such as copiers, printers and the like, relates to a high-speed, high-precision image forming apparatus producing very slight radiation noise and which is not susceptible to external noise, and further relates to an image forming apparatus of the type which transmits image signals by optical fiber.
The housing of an image forming apparatus such as a digital copier, laser printer and the like accommodates various types of structural elements including parts (print engine) directly related to actually forming a visible image such as photosensitive drum, laser oscillator, polygonal mirror, laser driver and the like, devices for receiving electrical signals for forming an image from external devices (or scanner), paper supply device, and various controllers for controlling these elements.
These structural elements cannot be freely arranged since the size of the housing itself is limited to achieve a compact form-factor similar to other office equipment. For this reason the elements which must be mutually separated for whatever reason are connected by cables used to transmit electrical signals.
Since the electrical signals transmitted over these cables include not only the high fundamental frequency of the signal itself which transmits much information, but also includes a large amount of the high-frequency component of digital signals, and when the cable is long, strong electromagnetic waves (noise) are emitted from the cable such that this noise itself as well as noise from other office equipment may cause operation errors.
A long cable may cause misshaping of the waveform of the signals transmitted over the cable, such that the signals may be recognized as errors on the receiving side so as to cause operation errors. Furthermore, there is concern that a long cable may function as an antenna collecting noise from outside the housing as well as inside the housing, so as to cause operation error in the apparatus.
Although these problems can be eliminated by providing shielding for the housing as well as between elements, shielding produces other problems by not only increasing the weight and volume of the apparatus and adversely affecting thermal efficiency, but also increasing the maintenance load, and increasing the cost of the apparatus.
The cables electrically connecting the print engine and video controller in image forming apparatuses are often relatively long due to the layout restrictions. Furthermore, since these cables carry the information of each pixel of an image across the entire image, they must transmit an extremely huge quantity of data having a high fundamental frequency which easily produces the previously described problems.
In the field of image forming apparatuses, on the other hand, there is strong demand for higher-speed image formation. In response to this demand much effort has been expended to increase the laser beam scanning speed, but as a result we must wait for solutions to problems of peripheral art including improving laser responsiveness, improving (accelerating) scanning signal generation speed, increasing the rotation speed of the polygonal mirror and the like.
This improvement does not pertain to simple improvement of scanning speed using a single laser beam as used heretofore, but pertains to simultaneous scanning by a plurality of laser beams (multi-beam scanning method). The multi-beam scanning method uses a plurality of laser beam light sources, wherein the laser beams emitted from the light sources simultaneously scan the surface of a photosensitive drum via an optical deflecting means such as a single polygonal mirror or the like.
Such a method is advantageous in that image formation can be accomplished as a speed of a multiple corresponding to the number of laser light sources with the previously described current art as is.
In this case, normally, a plurality of laser diodes are used, and the laser beam from each laser diode provided to a video controller is directed to a polygonal mirror of the print engine by a respective optical fiber.
Since electrical signals are not used in the signal transfers between the print engine and video controller as previously described, stable operation can be expected and image forming speed can be improved by using, for example, optical fiber within the housing, so as to not receive electrical noise from outside the housing even though there are electrical noise generation sources outside the housing.
Since the optical fibers discussed above used within the housing accommodate only several laser beams (or tens of beams in some cases), the thickness of the entire bundle of optical fibers cannot be ignored, and problems arise in the complexity of the task of handling and assembling these optical fibers. This method cannot be said to be adequate because the synchronizing signal is light reflected by an SOS mirror on the print engine side which is received by an SOS sensor, and the received light signal is electrically transmitted to the print engine side and may be affected by external noise from the electrical line used for this transmission, or this electrical line may emit noise. Furthermore, as for the signal used for synchronization there is no difference using the electrical signal line, and the task remains of handling and assembling this line.
In regard to the previously described problems there is no difference in using the line within the housing when one considers the signal line used for synchronization as a separate optical fiber. The present invention does not use a separate optical fiber, i.e., does not use a special optical fiber, and not only transmits signals including image information and synchronizing signals (radiation light for obtaining synchronizing signal) using a single optical fiber, but also transmits a synchronizing signal reflected by the SOS mirror on the print engine side simultaneously over a reverse path to the video controller. Furthermore, the present invention provides an image forming apparatus capable of reducing the number of lines (electrical signal lines and optical fiber) used in the housing, reducing external noise and emitted noise, and the interior of the image forming apparatus is consolidated making handling and assembly easier.
According to one embodiment, the present invention provides an image forming apparatus provided with a transmission means for sending optical signals over optical fiber, and an optical scanning device for scanning an object using an optical beam emitted from the optical fiber and detecting the optical beam at a detection position provided outside the image region, and synchronizing the main scan direction based on the detected beam, wherein the synchronizing optical output detected at the detection position is subjected to wavelength conversion by a wavelength converting means, and bi-directional communication is accomplished using the same optical fiber transmitting the optical signals.
A second solution means of the present invention provides an image forming apparatus provided with a transmission means for sending optical signals over optical fiber, a synchronizing optical output means for synchronization, wherein the wavelength of the synchronizing optical output is different from the wavelength of the optical signal transmitted by the transmission means, and an optical scanning device for scanning an object using an optical beam emitted from the optical fiber, and detecting the optical beam emitted by the synchronizing optical output means at a detection position provided outside the image region, and synchronizing the main scan direction based on the detected beam, wherein bi-directional communication is accomplished over the same optical fiber transmitting the optical signals by the transmission means and the synchronizing optical output at the detection position.